Pumice-containing remedial compositions and methods of use

ABSTRACT

Methods and compositions are provided that utilize pumice and various additives. An embodiment provides a method of remedial cementing in a subterranean formation comprising: providing a lightweight settable composition comprising pumice, a calcium activator, and water, wherein the lightweight settable composition has a density of less than about 13.5 pounds per gallon and is free of Portland cement; and using the lightweight settable composition in a remedial cementing method to seal one or more voids in a well bore. Also provided are pumice-containing remedial compositions and systems for remedial cementing.

BACKGROUND

The present invention relates to cementing operations and, moreparticularly, in certain embodiments, to methods and compositions thatutilize pumice and various additives.

In cementing operations, such as well construction and remedialcementing, settable compositions are commonly utilized. As used herein,the term “settable composition” refers to a composition thathydraulically sets or otherwise develops compressive strength. Settablecompositions may be used in primary cementing operations whereby pipestrings, such as casing and liners, are cemented in well bores. In atypical primary cementing operation, a settable composition may bepumped into an annulus between the exterior surface of the pipe stringdisposed therein and the walls of the well bore (or a larger conduit inthe well bore). The settable composition may set in the annular space,thereby forming an annular sheath of hardened, substantially impermeablematerial (e.g., a cement sheath) that may support and position the pipestring in the well bore and may bond the exterior surface of the pipestring to the well bore walls (or the larger conduit). Among otherthings, the cement sheath surrounding the pipe string should function toprevent the migration of fluids in the annulus, as well as protectingthe pipe string from corrosion. Settable compositions also may be usedin remedial cementing methods, such as in squeeze cementing for sealingvoids in a pipe string, cement sheath, gravel pack, subterraneanformation, and the like.

In remedial cementing, settable compositions may be used for sealingvoids in a pipe string or a cement sheath. As used herein the term“void” refers to any type of space, including fractures, holes, cracks,channels, spaces, and the like. Such voids may include: holes or cracksin the pipe strings; holes, cracks, spaces, or channels in the cementsheath; and very small spaces (commonly referred to as “microannuli”)between the cement sheath and the exterior surface of the well casing orformation. Sealing such voids may prevent the undesired flow of fluidse.g., oil, gas, water, etc.) and/or fine solids into, or from, the wellbore. The sealing of such voids, whether or not made deliberately, hasbeen attempted by introducing a substance into the void and permittingit to remain therein to seal the void. If the substance does not fitinto the void, a bridge, patch, or sheath may be formed over the void topossibly produce a termination of the undesired fluid flow. Substancesused heretofore in methods to terminate the undesired passage of fluidsthrough such voids include settable compositions comprising water andhydraulic cement, wherein the methods employ hydraulic pressure to forcethe settable composition into the void. Once placed into the void, thesettable composition may be permitted to harden.

Remedial cementing operations also may be used to seal portions ofsubterranean formations or portions of gravel packs. The portions of thesubterranean formation may include permeable portions of a formation andfractures (natural or otherwise) in the formation and other portions ofthe formation that may allow the undesired flow of fluid into, or from,the well bore. The portions of the gravel pack include those portions ofthe gravel pack, wherein it is desired to prevent the undesired flow offluids into, or from, the well bore. A “gravel pack” is as term commonlyused to refer to a volume of particulate materials (such as sand) placedinto a well bore to at least partially reduce the migration ofunconsolidated formation particulates into the well bore. Whilescreenless gravel packing operations are becoming more common, gravelpacking operations commonly involve placing a gravel pack screen in thewell bore neighboring a desired portion of the subterranean formation,and packing the surrounding annulus between the screen and the well borewith particulate materials that are sized to prevent and inhibit thepassage of formation solids through the gravel pack with producedfluids. Among other things, this method may allow sealing of the portionof the gravel pack to prevent the undesired flow of fluids withoutrequiring the gravel pack's removal.

A broad variety of settable compositions have been used heretofore,including cement compositions comprising Portland cement. Portlandcement is generally prepared from a mixture of raw materials comprisingcalcium oxide, silicon oxide, aluminum oxide, ferric oxide, andmagnesium oxide. The mixture of the raw materials is heated in a kiln toapproximately 2700° F., thereby initiating chemical reactions betweenthe raw materials. In these reactions, crystalline compounds, dicalciumsilicates, tricalcium silicates, tricalcium aluminates, and tetracalciumaluminoferrites, are formed. The product of these reactions is known asa clinker. The addition of a gypsum/anhydrate mixture to the clinker andthe pulverization of the mixture results in a fine powder that willreact to form a slurry upon the addition of water.

There are drawbacks, however, to the conventional preparation and use ofPortland cement. The energy requirements to produce Portland cement arequite high, and heat loss during production can further cause actualenergy requirements to be even greater. These factors contributesignificantly to the relatively high cost of Portland cement. Generally,Portland cement is as major component of the cost of hydraulic cementcompositions that comprise Portland cement. Recent Portland cementshortages, however, have further contributed to the rising cost ofhydraulic cement compositions that comprise Portland cement.

SUMMARY

An embodiment provides a method of remedial cementing in a subterraneanformation comprising: providing a lightweight settable compositioncomprising pumice, a calcium activator, and water, wherein thelightweight settable composition has a density of less than about 13.5pounds per gallon and is free of Portland cement; and using thelightweight settable composition in a remedial cementing method to sealone or more voids in a well bore.

Another embodiment provides a pumice-containing remedial settablecomposition comprising: pumice; a calcium activator; and water, whereinthe lightweight settable composition has a density of less than about13.5 pounds per gallon, and wherein the lightweight settable compositionis free of Portland cement.

Yet another embodiment provides a system for remedial cementingcomprising: a lightweight settable composition comprising pumice, acalcium activator, and water, wherein the lightweight settablecomposition has a density of less than about 13.5 pounds per gallon;mixing equipment for mixing the lightweight settable composition, andpumping equipment for delivering the lightweight settable composition toa well bore.

The features and advantages of the present invention will be readilyapparent to those skilled in the art. While numerous changes may be madeby those skilled in the art, such changes are within the spirit of theinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention disclose lightweight settablecompositions comprising pumice, a calcium activator, and water, whereinthe lightweight settable compositions are free of Portland cement. Otheradditives that may be included in the lightweight settable compositionsinclude shale, zeolite, amorphous silica, fly ash, metakaolin, perlite,rice hull ash, and/or swellable particulate elastomer. One of the manypotential advantages of embodiments of the lightweight settablecomposition is that pumice is a relatively inexpensive component incomparison to traditional cements such as Portland cement. Anotheradvantage is that pumice manufacture and subsequent use in a settablecomposition is less environmentally damaging as compared to cements suchas Portland cement. Therefore, a pumice settable composition would havea smaller carbon footprint. One more additional advantage is that thepumice-containing settable compositions are lightweight and fastsetting. Accordingly, embodiments of the lightweight settablecompositions may be used in a variety of subterranean applications forremedial cementing operations such in squeeze cementing for sealingvoids in a pipe string, cement sheath, gravel pack, subterraneanformation, and the like.

In some embodiments, the lightweight settable compositions may comprisepumice. Generally, pumice is a volcanic rock that exhibits cementitiousproperties, in that it may set and harden in the presence of a calciumactivator and water. The calcium activator may be used in combinationwith the pumice, for example, to provide sufficient calcium ions for thepumice to set. The pumice may also be ground, for example, Generally,the pumice may have any particle size distribution as desired for aparticular application. In certain embodiments, the pumice may have amean particle size in a range of from about 1 micron to about 200microns. The mean particle size corresponds to d50 values as measured byparticle size analyzers such as the manufactured by Malvern Instruments,Worcestershire, United Kingdom. In specific embodiments, the pumice mayhave a mean particle size in a range of from about 1 micron to about 200micron, from about 5 microns to about 100 microns, or from about 10micron to about 50 microns. In one particular embodiment, the pumice mayhave a mean particle size of less than about 15 microns. An example of asuitable pumice is DS-200 lightweight aggregate available from HessPumice Products, Inc., Malad City, Idaho, having an average particlesize of less than 20 microns. In some embodiments, a total amount ofcementitious components in the settable composition may consistessentially or and/or consist of the pumice. One a ordinary skill in theart, with the benefit of this disclosure, will recognize the appropriateamount of the pumice to include for a chosen application.

In some embodiments, the settable compositions may comprise a calciumactivator. The term “calcium activator” refers to a material thatgenerates calcium ions when mixed with water. The pumice reacts with thecalcium ions to react and form a hardened mass. The calcium activatormay be included in the settable compositions to provide calcium ions foractivation of the pumice, thus providing a settable composition thatreact with the water to form a hardened mass in accordance withembodiments of the present invention. Any of a variety of suitablecalcium activators may be used that are capable of generating calciumions when dissolved in the water. Examples of suitable calciumactivators include calcium formate, lime (e.g., hydrated lime), and anycombination thereof. In some embodiments, the calcium activators may bepresent in the settable compositions in an amount in the range of fromabout 0.1% to about 25% by weight of the pumice. In further embodiments,the calcium activator may be included in an amount in the range of fromabout 1% to about 10% by weight of the pumice.

In some embodiments, the settable compositions may be free of Portlandcement. In some embodiments, the settable compositions may beessentially free of any additional cementitious materials, such ashydraulic cements, including, but not limited to, those comprisingcalcium, aluminum, silicon, oxygen, iron, and/or sulfur, which set andharden by reaction with water. Specific examples of hydraulic cementsinclude, but are not limited to, Portland cements, pozzolana cements,gypsum cements, high alumina content cements, silica cements, and anycombination thereof. In some embodiments, the Portland cements areclassified as Classes A, C, H, or G cements according to AmericanPetroleum Institute, API Specification for Materials and Testing forWell Cements, API Specification 10, Fifth Ed., Jul. 1, 1990. Inaddition, in some embodiments, the hydraulic cement may include cementsclassified as ASTM Type I, II, or III. In some embodiments, the settablecompositions may comprise additional cementitious materials in an amountless than about 1% by weight of the pumice and, alternatively, less thanabout 0.1% by weight of the pumice.

The water used in embodiments of the settable compositions of thepresent invention may include, for example, freshwater, saltwater (e.g.,water containing one or more salts dissolved therein), brine (e.g.,saturated saltwater produced from subterranean formations), seawater, orany combination thereof. Generally, the water may be from any source,provided, for example, that it does not contain an excess of compoundsthat may undesirably affect other components in the settablecompositions. In some embodiments, the water may be included in anamount sufficient to form a pumpable slurry. In some embodiments, thewater may be included in the settable compositions of the presentinvention in an amount in a range of from about 40% to about 200% byweight of the pumice, In some embodiments, the water may be included inan amount in a range of from about 40% to about 150% by weight of thepumice.

Embodiments of the lightweight settable compositions may be foamed witha foaming additive and a gas, for example, to provide a composition witha reduced density. In some embodiments, the lightweight settablecomposition may be foamed to have a density of less than about 12 poundsper gallon (“lbs/gal”), less than about 11 lbs/gal, or less than about10 lbs/gal. In some embodiments, the lightweight settable compositionmay be foamed to have a density in a range of from about from about 4lbs/gal to about 12 lbs/gal and, alternatively, about 7 lbs/gal to about9 lbs/gal. The gas used for foaming the lightweight settablecompositions may be any suitable gas for foaming the lightweightsettable composition, including, but not limited to air, nitrogen, andcombinations thereof. Generally, the gas should be present inembodiments of the foamed lightweight settable composition in an amountsufficient to form the desired foam. In certain embodiments, the gas maybe present in an amount in the range of from about 5% to about 80% byvolume of the foamed lightweight settable composition at atmosphericpressure, alternatively, about 5% to about 55% by volume, and,alternatively, about 15% to about 30% by volume.

Foaming additives may be included in embodiments of the lightweightsettable compositions to, for example, facilitate foaming and/orstabilize the resultant foam formed therewith. Examples of suitablefoaming additives include, but are not limited to: mixtures of anammonium salt of an alkyl ether sulfate, a cocoamidopropyl betainesurfactant, a cocoamidopropyl dimethylamine oxide surfactant, sodiumchloride, and water; mixtures of an ammonium salt of an alkyl ethersulfate surfactant, a cocoamidopropyl hydroxysultaine surfactant, acocoamidopropyl dimethylamine oxide surfactant, sodium chloride, andwater; hydrolyzed keratin; mixtures of an ethoxylated alcohol ethersulfate surfactant, an alkyl or alkene amidopropyl betaine surfactant,and an alkyl or alkene dimethylamine oxide surfactant; aqueous solutionsof an alpha-olefinic sulfonate surfactant and a betaine surfactant; andcombinations thereof. An example of a suitable foaming additive isZONESEALANT™ 2000 agent, available from Halliburton Energy Services,Inc.

As previously mentioned, embodiments of the lightweight settablecompositions may include one or more additives selected from shale,zeolite, amorphous silica, fly ash, metakaolin, perlite, rice hull ash,and/or swellable elastomers. These additives may be included in thelightweight settable compositions to improve one or more properties,including mechanical properties such as compressive strength.

In certain embodiments, the lightweight settable compositions of thepresent invention may comprise shale in an amount sufficient to providethe desired compressive strength, density, and/or cost. A variety ofshales are suitable, including those comprising silicon, aluminum,calcium, and/or magnesium. Suitable examples of shale include, but arenot limited to, PRESSUR-SEAL® FINE LCM material and PRESSUR-SEAl® COARSELCM material, which are commercially available from TXI Energy Services,Inc., Houston, Tex. Generally, the shale may have any particle sizedistribution as desired for as particular application. In certainembodiments, the shale may have a particle size distribution in therange of about 37 microns to about 4,750 microns. In some embodimentsthe shale may be vitrified shale. In some embodiments the shale may becalcined shale. In certain embodiments, the shale may be present in thelightweight settable compositions of the present invention in an amountin the range of from about 0.1% to about 100% by weight of the pumice.In some embodiments, the shale may be present in an amount rangingbetween any of and/or including any of about 10%, about 20%, about 30%,about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, orabout 100% by weight of the pumice. One of ordinary skill in the art,with the benefit of this disclosure, will recognize the appropriateamount of the shale to include for a chosen application.

In certain embodiments, the lightweight settable compositions of thepresent invention may comprise zeolite. Zeolite may be used inconjunction with the shale in some embodiments. In other embodiments,zeolite may be an alternative to shale. The choice may be dictated by anumber of factors, such as total extent of compressive strength of thecement, time for cement composition to develop compressive strength, anddensity of the composition. Zeolites generally are porousalumino-silicate minerals that may be either as natural or syntheticmaterial. Synthetic zeolites are based on the same type of structuralcell as natural zeolites, and may comprise aluminosilicate hydrates. Asused herein, the term “zeolite”refers to all natural and synthetic formsof zeolite. In certain embodiments, the zeolite may be present in thelightweight settable compositions of the present invention in an amountin the range of from about 0.1% to about 100% by weight of the pumice.In some embodiments, the zeolite may be present in an amount rangingbetween any of and/or including any of about 10%, about 20%, about 30%,about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, orabout 100% by weight of the pumice. One of ordinary skill in the art,with the benefit of this disclosure, will recognize the appropriateamount of the zeolite to include for a chosen application.

In certain embodiments, the lightweight settable compositions of thepresent invention may comprise amorphous silica. Amorphous silica isgenerally a byproduct of a ferrosilicon production process, wherein theamorphous silica may be formed by oxidation and condensation of gaseoussilicon suboxide, SiO, which is formed as an intermediate during theprocess. An example of a suitable source of amorphous silica isSILICALITE™, available from Halliburton Energy Services, Inc. In certainembodiments, the amorphous silica may be present in the lightweightsettable compositions of the present invention in an amount in the rangeof from about 0.1% to about 40% by weight of the pumice. In someembodiments, the amorphous silica may be present in an amount rangingbetween any of and/or including any of about 10%, about 20%, about 30%,and about 40% by weight of the pumice. One of ordinary skill in the art,with the benefit of this disclosure, will recognize the appropriateamount of the shale to include for a chosen application,

Fly ash may be included in embodiments of the lightweight settablecompositions of the present invention. A variety of fly ashes may besuitable, including fly ash classified as Class C and Class F fly ashaccording to American Petroleum Institute, API Specification forMaterials and Testing for Well Cements, API Specification 10, Fifth Ed.,Jul. 1, 1990, Class C fly ash comprises both silica and lime so that,when mixed with water, it sets to form a hardened mass. Class F fly ashgenerally does not contain sufficient lime, so an additional source ofcalcium ions may be required for the Class F fly ash to form a settablecomposition with water. In some embodiments, lime may be mixed withClass F fly ash in an amount in the range of about 0.1% to about 25% byweight of the fly ash. In some instances, the lime may be hydrated lime.Suitable examples of fly ash include, but are not limited to, POZMIX® Acement additive, available from Halliburton Energy Services, Inc. Wherepresent, the fly ash generally may be included in the lightweightsettable compositions in an amount sufficient to provide the desiredcompressive strength, density, and/or cost. In certain embodiments, thefly ash may be present in the lightweight settable compositions of thepresent invention in an amount in the range of from about 0.1% to about100% by weight of the pumice. In some embodiments, the fly ash may bepresent in an amount ranging between any of and/or including any ofabout 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about70%, about 80%, about 90%, or about 100% by weight of the pumice. One ofordinary skill in the art, with the benefit of this disclosure, willrecognize the appropriate amount of the fly ash to include for a chosenapplication,

Metakaolin may be included in embodiments of the lightweight settablecompositions of the present invention. Generally, metakaolin is a whitepozzolan that may be prepared by heating kaolin clay, for example, totemperatures in the range of about 600° C. to about 800° C. In certainembodiments, the metakaolin may be present in the lightweight settablecompositions of the present invention in an amount in the range of fromabout 0.1% to about 100% by weight of the pumice. In some embodiments,the metakaolin may be present in an amount ranging between any of and/orincluding any of about 10%, about 20%, about 30%, about 40%, about 50%,about 60%, about 70%, about 80%, about 90%, or about 100% by weight ofthe pumice. One of ordinary skill in the art, with the benefit of thisdisclosure, will recognize the appropriate amount of the metakaolin toinclude for a chosen application.

Perlite may be included in embodiments of the lightweight settablecompositions of the present invention. Perlite is an ore and generallyrefers to a naturally occurring volcanic, amorphous siliceous rockcomprising mostly silicon dioxide and aluminum oxide. Perlite suitablefor use in embodiments of the present invention includes expandedperlite and unexpanded perlite. Examples of suitable perlite includeexpanded and/or unexpanded perlite. The expanded or unexpanded perlitemay also be ground, for example. In certain embodiments, the perlite maybe present in the lightweight settable compositions of the presentinvention in an amount in the range of from about 0.1% to about 100% byweight of the pumice. In some embodiments, the perlite may be present inan amount ranging between any of and/or including any of about 10%,about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about80%, about 90%, or about 100% by weight of the pumice. One of ordinaryskill in the art, with the benefit of this disclosure, will recognizethe appropriate amount or the perlite to include for a chosenapplication.

Rice hull ash may be included in embodiments of the lightweight settablecompositions of the present invention. In general, rice hull ash is theash produced from the burning of rice hulls, which are the hardcoverings of grains of rice, and may comprise primarily silica andcarbon. In certain embodiments, the rice hull ash may be present in thelightweight settable compositions of the present invention in an amountin the range of from about 0.1% to about 100% by weight of the pumice.In some embodiments, the rice hull ash may be present in an amountranging between any of and for including any of about 10%, about 20%,about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about90%, or about 100% by weight of the pumice. One of ordinary skill in theart, with the benefit of this disclosure, will recognize the appropriateamount of the rice hull ash to include for a chosen application.

A swellable particulate elastomer may be included in embodiments of thelightweight settable compositions of the present invention. Particulateelastomers suitable for use in embodiments of the present invention maygenerally swell by up to about 100% of their original size at thesurface when contacted by oil. Under downhole conditions, this swellingmay be more, or less, depending on the conditions presented. Forexample, the swelling may be at least 10% at downhole conditions, insome embodiments, the swelling may be up to about 50% under downholeconditions. However, as those of ordinary skill in the art, with thebenefit of this disclosure, will appreciate, the actual swelling whenthe particulate elastomer is included in a lightweight settablecomposition may depend on, for example, the elastomer concentration,downhole pressure, and downhole temperature, among other factors. Somespecific examples of suitable particulate elastomers include, but notlimited to, natural rubber, acrylate butadiene rubber, polyacrylaterubber, isoprene rubber, chloroprene rubber, butyl robber (HR),brominated butyl rubber (BIIR), chlorinated butyl rubber (CIIR),chlorinated polyethylene (CM/CPE), neoprene rubber (CR), styrenebutadiene copolymer rubber (SBR), styrene butadiene block copolymerrubber, sulphonated polyethylene (CSM), ethylene acrylate rubber(EAM/AEM), epichlorohydrin ethylene oxide copolymer (CO, ECO),ethylene-propylene rubber (EPM and EDPM), ethylene-propylene- dieneterpolymer rubber (EPT), ethylene vinyl acetate copolymer,fluorosilicone rubbers (FVMQ), silicone rubbers (VMQ), poly2,2,1.-bicyclo heptene (polynorbornene), alkylstyrene, and crosslinkedvinyl acrylate copolymers. In certain embodiments, the swellableparticulate elastomer may be present in the lightweight settablecompositions of the present invention in an amount in the range of fromabout 0.1% to about 100% by weight of the pumice. In some embodiments,the swellable particulate elastomer may be present in an amount rangingbetween any of and/or including any of about 10%, about 20%, about 30%,about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, orabout 100% by weight of the pumice. One of ordinary skill in the art,with the benefit of this disclosure, will recognize the appropriateamount of the swellable particulate elastomer to include for a chosenapplication.

Other additives suitable for use in subterranean remedial cementingoperations may also be added to embodiments of the lightweight settablecompositions, in accordance with embodiments of the present invention.Examples of such additives include, but are not limited to,strength-retrogression additives, set accelerators, set retarders,lightweight additives, gas-generating additives, mechanical propertyenhancing additives, lost-circulation materials, fluid loss controladditives, defoaming additives, thixotropic additives, and anycombination thereof. Specific examples of these, and other, additivesinclude crystalline silica, fumed silica, silicates, silicalite, salts,fibers, hydratable clays, shale, microspheres, diatomaceous earth,natural pozzolan, cement kiln dust, resins, any combination thereof, andthe like. A person having ordinary skill in the art, with the benefit ofthis disclosure, will readily be able to determine the type and amountof additive useful for a particular application and desired result.

Strength-retrogression additives may be included in embodiments of thelightweight settable composition to, for example, prevent theretrogression of strength after the settable composition has beenallowed to develop compressive strength when the settable composition isexposed to high temperatures. These additives may allow the settablecompositions to form as intended, preventing cracks and prematurefailure of the cementitious composition. Examples of suitablestrength-retrogression additives may include, but are not limited to,amorphous silica, coarse grain crystalline silica, fine graincrystalline silica, or a combination thereof.

Set accelerators may be included in embodiments of the lightweightsettable compositions to, for example, increase the rate of settingreactions. Control of setting time may allow for the ability to adjustto well bore conditions or customize set times for individual jobs.Examples of suitable set accelerators may include, but are not limitedto, aluminum sulfate, alums, calcium chloride, calcium sulfate,gypsum-hemihydrate, sodium aluminate, sodium carbonate, sodium chloride,sodium silicate, sodium sulfate, ferric chloride, or a combinationthereof.

Set retarders may be included in embodiments of the lightweight settablecompositions to, for example, increase the thickening time of thesettable compositions. Examples of suitable set retarders include, butare not limited to, ammonium, alkali metals, alkaline earth metals,borax, metal salts of calcium lignosulfonate, carboxymethyl hydroxyethylcellulose, sulfoalkylated lignins, hydroxycarboxy acids, copolymers of2-acrylamido-2-methylpropane sulfonic acid salt and acrylic acid ormaleic acid, saturated salt, or a combination thereof. One example of asuitable sulfoalkylated lignin comprises a sulfomethylated lignin.

Lightweight additives may be included in embodiments of the lightweightsettable compositions to, for example, decrease the density of thesettable compositions. Examples of suitable lightweight additivesinclude, but are not limited to, bentonite, coal, diatomaceous earth,expanded perlite, fly ash, gilsonite, hollow microspheres, low-densityelastic beads, nitrogen, pozzolan-bentonite, sodium silicate,combinations thereof, or other lightweight additives known in the art.

Gas-generating additives may be included in embodiments of thelightweight settable compositions to release gas at a predeterminedtime, which may be beneficial to prevent gas migration from theformation through the settable composition before it hardens. Thegenerated gas may combine with or inhibit the permeation of the settablecomposition by formation gas. Examples of suitable gas-generatingadditives include, but are not limited to, metal particles (e.g.,aluminum powder) that react with an alkaline solution to generate a gas.

Mechanical-property-enhancing additives may be included in embodimentsof the lightweight settable compositions to, for example, ensureadequate compressive strength and long-term structural integrity. Theseproperties can be affected by the strains, stresses, temperature,pressure, and impact effects from a subterranean environment. Examplesof mechanical property enhancing additives include, but are not limitedto, carbon fibers, glass fibers, metal fibers, mineral fibers, silicafibers, polymeric elastomers, and latexes.

Lost-circulation materials may be included in embodiments of thelightweight settable compositions to, for example, help prevent the lossof fluid circulation into the subterranean formation. Examples oflost-circulation materials include but are not limited to, cedar bark,shredded cane stalks, mineral fiber, mica flakes, cellophane, calciumcarbonate, ground rubber, polymeric materials, pieces of plastic,grounded marble, wood, nut hulls, formica, corncobs, and cotton hulls.

Fluid-loss-control additives may be included in embodiments of thelightweight settable compositions to, for example, decrease the volumeof fluid that is lost to the subterranean formation. Properties of thesettable compositions may be significantly influenced by their watercontent. The loss of fluid can subject the settable compositions todegradation or complete failure of design properties. Examples ofsuitable fluid-loss-control additives include, but not limited to,certain polymers, such as hydroxyethyl cellulose,carboxymethylhydroxyethyl cellulose, copolymers of2-acrylamido-2-methylpropanesulfonic acid and acrylamide orN,N-dimethylacrylamide, and graft copolymers copolymers a backbone oflignin or lignite and pendant groups comprising at least one memberselected from the group consisting of2-acrylamido-2-methylpropanesulfonic acid, acrylonitrile, andN,N-dimethylacrylamide.

Defoaming additives may be included in embodiments of the lightweightsettable compositions to, for example, reduce tendency for the settablecomposition to foam during mixing and pumping of the settablecompositions. Examples of suitable defoaming additives include, but arenot limited to, polyol silicone compounds. Suitable defoaming additivesare available from Halliburton Energy Services, Inc., under the productname D-AIR™ defoamers.

Thixotropic additives may be included in embodiments of the lightweightsettable compositions to, for example, provide a settable compositionthat can be pumpable as a thin or low viscosity fluid, but when allowedto remain quiescent attains a relatively high viscosity. Among otherthings, thixotropic additives may be used to help control free water,create rapid gelation as the slurry sets, combat lost circulation,prevent “fallback” in annular column, and minimize gas migration.Examples of suitable thixotropic additives include, but are not limitedto, gypsum, water soluble carboxyalkyl, hydroxyalkyl, mixed carboxyalkylhydroxyalkyl either of cellulose, polyvalent metal salts, zirconiumoxychloride with hydroxyethyl cellulose, or a combination thereof.

Those of ordinary skill in the art will appreciate that the lightweightsettable compositions generally may be characterized as lightweight inthat the settable compositions have a density that does not exceed about13.5 lb/gal. Because the settable compositions are lightweight, they maybe used in applications where heavier compositions may not be suitable,for example, those with fracture gradients that would be exceed by theheavier compositions. Lightweight settable compositions may also beused, for example, to prevent the collapse of depleted zones that mayresults from a heavier composition. In an exemplary embodiment, thedensity of the settable compositions is about 12.5 lb/gal. Those ofordinary skill in the art, with the benefit of this disclosure, willrecognize the appropriate density for a particular application.

The components of the lightweight settable composition may be combinedin any order desired to form a settable composition that can be placedinto a subterranean formation. In addition, the components of thesettable compositions may be combined using any mixing device compatiblewith the composition, including a bulk mixer, for example. In someembodiments, the settable compositions may be prepared by combining thethy components with water. Other additives may be combined with thewater before it is added to the dry components. In some embodiments, thedry components may be dry blended prior to their combination with thewater. in some embodiments, a dry blend may be prepared that comprisesthe pumice. The dry blend may also comprise one or more of shale,zeolite, amorphous silica, fly ash, metakaolin, perlite, rice hull ash,and/or swellable particulate elastomer. The calcium-ion source may beadded, for example, to the water or the dry blend. Other suitabletechniques may be used for preparation of the setting compositions aswill be appreciated by those of ordinary skill in the art in accordancewith embodiments of the present invention.

In remedial cementing embodiments, the lightweight settable compositionsmay be used, for example, in squeeze-cementing operations. By way ofexample, the settable compositions may be placed in a well bore to pluga void or crack in the formation, in a gravel pack, in the conduit, inthe cement sheath, and/or a microannulus between the cement sheath andthe conduit.

An example of a method of the present invention is method of sealing aportion of a gravel pack or a portion of a subterranean formation. Anexample of such a method may comprise providing a lightweight settablecomposition; introducing the lightweight settable composition into theportion of the gravel pack or the portion of the subterranean formation;and allowing the lightweight settable composition to form a hardenedmass in the portion. The portions of the subterranean formation mayinclude permeable portions of the formation and fractures (natural orotherwise) in the formation and other portions of the formation that mayallow the undesired flow of fluid into, or from, the well bore. Theportions of the gravel pack include those portions of the gravel pack,wherein it is desired to prevent the undesired flow of fluids into, orfrom, the well bore. Among other things, this method may allow thesealing of the portion of the gravel pack to prevent the undesired flowof fluids without requiring the gravel pack's removal.

Another example of a method of the present invention is a method ofsealing voids located in a pipe string(e.g., casing, expandable casings,liners, etc,) or in a cement sheath. Generally, the pipe string will bedisposed in a well bore, and the cement sheath may be located in theannulus between the pipe string disposed in the well bore and a wall ofthe well bore. An example of such a method may comprise providing alightweight settable composition: introducing the lightweight settablecomposition into the void; and allowing the lightweight settablecomposition to set to form a hardened mass in the void.

When sealing a void in a pipe string, the methods of the presentinvention, in some embodiments, further may comprise locating the voidin the pipe string; and isolating the void by defining a space withinthe pipe string in communication with the void; wherein the lightweightsettable composition may be introduced into the void from the space. Thevoid may be isolated using any suitable technique and/or apparatus,including bridge plugs, packers, and the like. The void in the pipestring may be located using any suitable technique.

When sealing a void in the cement sheath, the methods of the presentinvention, in some embodiments, further may comprise locating the voidin the cement sheath; producing a perforation in the pipe string thatintersects the void; and isolating the void by defining a space withinthe pipe string in communication with the void via the perforation,wherein the lightweight settable composition is introduced into the voidvia the perforation. The void in the pipe string may be located usingany suitable technique. The perforation may be created in the pipestring using any suitable technique, for example, perforating guns. Thevoid may be isolated using any suitable technique and/or apparatus,including bridge plugs, packers, and the like.

In some embodiments, the lightweight settable compositions may set tohave a desirable compressive strength for remedial cementing operations.Compressive strength is generally the capacity of as material orstructure to withstand axially directed pushing forces. The compressivestrength may be measured at a specified time after the settablecompositions have been positioned and the settable compositions aremaintained under specified temperature and pressure conditions.Compressive strength can be measured by either a destructive method ornon-destructive method. The destructive method physically tests thestrength of treatment fluid samples at various points in time bycrushing the samples in a compression-testing machine. The compressivestrength is calculated from the failure load divided by thecross-sectional area resisting the load and is reported in units ofpound-force per square inch (psi). Non-destructive methods typically mayemploy an Ultrasonic Cement Analyzer (“UCA”), available from FannInstrument Company, Houston, Tx. Compressive strengths may be determinedin accordance with API RP 10B-2, Recommended Practice Testing WellCements, First Edition, Jul. 2005.

By way of example, the lightweight settable compositions, may develop a24-hour compressive strength—after mixing of the dry blend with thewater—in the range of from about 100 psi to about 165 psi,alternatively, from about 80 psi to about 165 psi, or alternatively fromabout 100 psi to about 600 psi. In some embodiments, the lightweightsettable composition may develop a compressive strength in 24 hours ofat least about 20 psi, at least about 100 psi, at least about 500 psi,or more.

The exemplary lightweight settable composition disclosed herein maydirectly or indirectly affect one or more components or pieces ofequipment associated with the preparation, delivery, recapture,recycling, reuse, and/or disposal of the disclosed settablecompositions. For example, the disclosed settable compositions maydirectly or indirectly affect one or more mixers, related mixingequipment, mud pits, storage facilities or units, compositionseparators, heat exchangers, sensors, gauges, pumps, compressors, andthe like used generate, store, monitor, regulate, and/or recondition theexemplary settable compositions. The disclosed settable compositions mayalso directly or indirectly affect any transport or delivery equipmentused to convey the settable compositions to a well site or downhole suchas, for example, any transport vessels, conduits, pipelines, trucks,tubulars, and/or pipes used to compositionally move the settablecompositions from one location to another, any pumps, compressors, ormotors (e.g., topside or downhole) used to drive the settablecompositions into motion, any valves or related joints used to regulatethe pressure or flow rate of the settable compositions, and any sensors(i.e., pressure and temperature), gauges, and/or combinations thereof,and the like. The disclosed settable compositions may also directly orindirectly affect the various downhole equipment and tools that may comeinto contact with the settable cement compositions such as, but notlimited to, wellbore casing, wellbore liner, completion string, insertstrings, drill string, coiled tubing, slickline, wireline, drill pipe,drill collars, mud motors, downhole motors and/or pumps, cement pumps,surface-mounted motors and/or pumps, centralizers, turbolizers,scratchers, floats (e.g., shoes, collars, valves, etc), logging toolsand related telemetry equipment, actuators (e.g., electromechanicaldevices, hydromechanical devices, etc.), sliding sleeves, productionsleeves, plugs, screens, filters, flow control devices (e.g., inflowcontrol devices, autonomous inflow control devices, outflow controldevices, etc.), couplings (e.g., electro-hydraulic wet connect, dryconnect, inductive coupler etc.), control lines (e.g. electrical, fiberoptic, hydraulic, etc.), surveillance lines, drill bits and reamers,sensors or distributed sensors, downhole heat exchangers, valves andcorresponding actuation devices, tool seals, packers, cement plugs,bridge plugs, and other wellbore isolation devices, or components, andthe like.

EXAMPLES

To facilitate a better understanding of the present invention, thefollowing examples of some of the preferred embodiments are given. In noway should such examples be read to limit, or to define, the scope ofthe invention.

Example 1

The following series of tests were performed to evaluate the mechanicalproperties of the lightweight settable compositions. Twelve differentlightweight settable compositions, designated Samples 1-12, wereprepared using the indicated amounts of water, pumice, lime, shale,and/or zeolite. The amounts of these components are indicated in thetable below with percent by weight of blend (“% bwob”) indicating thepercent of the component by weight of the blend of pumice, shale, and/orzeolite. The pumice used for the tests was either DS 200 or DS 325lightweight aggregate available from Hess Pumice Products, Malad City,Id. The lime used for the tests was Texas lime from Cleburne, Tex. Theshale and zeolite used for the tests were supplied by Magnablend, Inc.,Waxahachie, Tex. Sample 1 was a comparative composition that did notinclude lime as a calcium activator. This sample did not set (DNS) andtherefore possessed no measurable compressive strength (0 psi).

After preparation, the samples were allowed to cure for twenty-fourhours in a 2″ by 4″ metal cylinder that was placed in a water bath at140° F. to form set cylinders. Immediately after removal from the waterbath, destructive compressive strengths were determined using amechanical press in accordance with API RP 10B-2. The results of thistest are set forth below.

TABLE 1 Components 24 Hr Water Pumice Comp. Density (% DS 200 DS 325Lime Shale Zeolite Strength Sample (lb/gal) bwob) (% bwob) (% bwob) (%bwob) (% bwob) (% bwob) (psi) 1 12.5 75.06 — 100 0 — — DNS 2 12.5 78.65— 100 5 — — 112 3 12.5 82.24 — 100 10 — — 256 4 12.5 78.65 100 — 5 — —140 5 12.5 82.24 100 — 10 — — 218 6 12.5 57.47 100 — 10 — — DNS 7 12.581.38 50 — 2.5 50 — 110 8 12.5 94.97 50 — 5 50 — 162 9 12.5 77.18 50 — 525 25 96 10 12.5 78.98 50 — 7.5 25 25 338 11 12.5 80.78 50 — 10 25 25407 12 12.5 84.37 50 — 15 25 25 459

Based on the results of these tests, the inclusion of lime as a calciumactivator in the settable compositions had a significant impact oncompressive strength development. Likewise, the blending of the shaleand zeolite additives with the pumice, also produced significantcompressive strength gains.

Example 2

The following series of tests were performed to evaluate the mechanicalproperties of the lightweight settable compositions. Seven differentlightweight settable compositions, designated Samples 13-19, wereprepared using the indicated amounts of water, pumice, lime, fly ash,metakaolin, or perlite. The amounts of these components are indicated inthe table below with percent by weight of blend (“% bwob”) indicatingthe percent of the component by weight of the blend of pumice, fly ash,metakaolin, and/or perlite. The pumice used for the tests was DNS 200lightweight aggregate available from Hess Pumice Products, Malad City,Id. The lime used for the tests was Texas lime from Cleburne. Tex. Thefly ash used for the samples was POZMIX® pozzolanic cement, availablefrom Halliburton Energy Services, Inc. The metakaolin used for the testswas METAMAX® pozzolanic cement additive, available from BASF. Theperlite used was ground, unexpanded perlite (IM-325), available fromHess Pumice Products, Malad City, Id.

After preparation, the samples were allowed to cure for twenty-fourhours in a 2″ by 4″ metal cylinder that was placed in a water bath at140° F. to form set cylinders. Immediately after removal from the waterbath, destructive compressive strengths were determined using amechanical press in accordance with API RP 10B-2. The results of thistest are set forth below.

TABLE 2 Components 24 Hr Water Lime Fly Ash Comp. Density (% Pumice (%(% Metakaolin Perlite Strength Sample (lb/gal) bwob) (% bwob) bwob)bwob) (% bwob) (% bwob) (psi) 13 12.5 86.44 80 15 20 — — 162 14 14 51.6850 15 50 — — 146 15 14 50.94 80 15 20 — — 88 16 12.5 89.97 50 10 — 50 —233 17 12.5 93.57 50 15 — 50 — 579 18 12.5 76.58 50 10 — — 50 273 1912.5 80.17 50 15 — — 50 259

Based on the results of these tests, the inclusion of metakaolinprovided the largest increase in compressive strength, with the valuescaling noticeably with the increase of lime. Perlite showed a lesserincrease. The fly ash showed either no increase or a negligible increaseas generally compared to the earlier samples without additives (samples4-6).

Example 3

The following series of tests were performed to evaluate the mechanicalproperties of the lightweight settable compositions. Six differentlightweight settable compositions, designated Samples 20-25, wereprepared using the indicated amounts of water, pumice, lime, rice hullash, amorphous silica, or swellable particulate elastomer. The amountsof these components are indicated in the table below with percent byweight of blend (“% bwob”) indicating the percent of the component byweight of the blend of pumice, rice hull ash, amorphous silica, and/orswellable particulate elastomer, The pumice used for the tests was DNS200 lightweight aggregate available from Hess Pumice Products, MaladCity, Id. The lime used for the tests was Texas lime from Cleburne, Tex.The rice hull ash used for the tests is available from Rice HullSpecialty Products Inc., Stuttgart, Ark. The amorphous silica used forthe tests was Silicalite™ cement additive, available from HalliburtonEnergy Services, Inc. The swellable particulate elastomer used for thetests was LIFECEM™ 100, available from Halliburton Energy Services, Inc.

After preparation, the samples were allowed to cure for twenty-fourhours in a 2″ by 4″ metal cylinder that was p aced in a at bath at 140°F. to form set cylinders. Immediately after removal from the water bath,destructive compressive strengths were determined using a mechanicalpress in accordance with API RP 10B-2. The results of this test are setforth below.

TABLE 3 Components 24 Hr Water Rice Hull Amorphous Comp. Density (%Pumice Lime Ash Silica Elastomer Strength Sample (lb/gal) bwob) (% bwob)(% bwob) (% bwob) (% bwob) (% bwob) (psi) 20 12.5 85.95 50 10 50 — — 17621 12.5 89.55 50 15 50 — — 208 22 12.5 83.43 80 10 — 20 — 426 23 12.587.02 80 15 — 20 — 557 24 12.5 65.78 90 10 — — 10 194 25 12.5 69.37 9015 — — 10 216

Based on the results of these tests, the inclusion of the amorphoussilica provided the largest increase in compressive strength, with thevalue scaling noticeably with the increase of lime. Both rice hull ashand the swellable elastomer showed a much smaller increase incompressive strength.

Example 4

The following series of tests were performed to evaluate the mechanicalproperties of the lightweight settable compositions after foaming with afoaming additive and a gas. Six different base lightweight settablecompositions, designated Samples 1-6, were prepared having a density of12.5 lbs/gal using the indicated amounts of water, pumice, lime, shale,and/or zeolite, or metakaolin, The amounts of these components areindicated in the tables below with percent by weight of blend (“% bwob”)indicating the percent of the component by weight of the blend ofpumice, shale, and/or zeolite. Every sample was then foamed by using afoaming additive (ZONESEALANT™ 2000 agent, available from HalliburtonEnergy Services, Inc) in an amount of 2% by weight of the water toprovide the foam density listed in the table below. The pumice used forthe tests was DS 200 lightweight aggregate available from Hess PumiceProducts, Malad City, Id. The lime used for the tests was Texas limefrom Cleburne Tex. The shale and zeolite used for the tests weresupplied by Magnablend, Inc., Waxahachie, Tex. The metakaolin used forthe tests was METAMAX® pozzolanic cement additive, available from BASF.Every foamed sample is as foamed version of a previous sample andcorresponds to another sample previously listed above. The foamedsamples are presented in Table 4.

After preparation, the samples were allowed to cure for twenty-fourhours in a 2″ by 4″ metal cylinder that was placed in a water bath at140°°F. to form set cylinders. Immediately after removal from the waterbath, destructive compressive strengths were determined using amechanical press in accordance with API RP 10B-2. The results of thistest are set forth below.

TABLE 4 Components 24 Hr Foam Water Comp. Foamed Density (% Pumice LimeShale Zeolite Metakaolin Strength Sample (lb/gal) bwob) (% bwob) (%bwob) (% bwob) (% bwob) (% bwob) (psi) 26 9.36 78.65 100 5 — — — 72 279.9 82.24 100 10 — — — 113 28 9.89 81.38 50 2.5 50 — — 73 29 9.88 94.9750 5 50 — — 20 30 9.48 84.37 50 15 25 25 — 238 31 9.54 93.57 50 15 — —50 193

For the sake of brevity, only certain ranges are explicitly disclosedherein. However, ranges from any lower limit may be combined with anyupper limit to recite a range not explicitly recited, as well as, rangesfrom any lower limit may be combined with any other lower limit torecite a range not explicitly recited, in the same way, ranges from anyupper limit may be combined with any other upper limit to recite a rangenot explicitly recited. Additionally, whenever a numerical range with alower limit and an upper limit is disclosed, any number and any includedrange falling within the range are specifically disclosed. Inparticular, every range of values (of the form, “from about a to aboutb,” or, equivalently, “from approximately a to b,” or, equivalently,“from approximately a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues even if not explicitly recited. Thus, every point or individualvalue may serve as its own lower or upper limit combined with any otherpoint or individual value or any other lower or upper limit, to recite arange not explicitly recited.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Although individual embodiments arediscussed, the invention covers all combinations of all thoseembodiments. Furthermore, no limitations are intended to the details ofconstruction or design herein shown, other than as described in theclaims below. Also, the terms in the claims have their plain, ordinarymeaning unless otherwise explicitly and clearly defined by the patentee.It is therefore evident that the particular illustrative embodimentsdisclosed above may be altered or modified and all such variations areconsidered within the scope and spirit of the present invention. Ifthere is any conflict in the usages of a word or term in thisspecification and one or more patent(s) or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

What is claimed is:
 1. A method of remedial cementing in a subterraneanformation comprising: providing a lightweight settable compositioncomprising pumice, a calcium activator, and water, wherein thelightweight settable composition has a density of less than about 13.5pounds per gallon and is essentially free of any additional cementitiouscomponents, wherein the water is present in an amount in a range of fromabout 40% to about 200% by weight of the pumice, wherein the lightweightsettable composition is foamed with a foaming additive and a gas; andplacing the lightweight settable composition into a void or crack in thesubterranean formation, a gravel pack, a conduit, a cement sheath, or amicroannulus.
 2. The method of claim 1, wherein the calcium activator ispresent in an amount of about 0.1% to about 25% by weight of the pumice.3. The method of claim 1, wherein the calcium activator comprises amaterial selected from the group consisting of calcium formate, lime,hydrated lime, and any combination thereof.
 4. The method of claim 1,wherein the lightweight settable composition further comprises at leastone additive selected from the group consisting of shale, zeolite,amorphous silica, fly ash, metakaolin, perlite, rice hull hush, aswellable particulate elastomer, and any combination thereof.
 5. Themethod of claim 4, wherein the at least one additive is present in anamount in a range of from about 0.1% to about 100% by weight of thepumice.
 6. The method of claim 4, wherein the at least one additivepresent in an amount in a range of from about 50% to about 100% byweight of the pumice.
 7. The method of claim 1, wherein the lightweightsettable composition further comprises shale in an amount of about 40%to about 100% by weight of the pumice, and wherein the light weightsettable composition further comprises zeolite in an amount of about 40%to about 100% by weight of the pumice.
 8. The method of claim 1, whereinthe lightweight settable composition further comprises metakaolin in anamount of about 40% to about 100% by weight of the pumice.
 9. The methodof claim 1, where the lightweight settable composition further comprisesat least one additive selected from the group consisting ofstrength-retrogression additives, set accelerators, set retarders,lightweight additives, gas-generating additives, mechanical propertyenhancing additives, lost-circulation materials, fluid loss controladditives, foaming additives, defoaming additives, thixotropicadditives, and any combination thereof.
 10. The method of claim 1,wherein the lightweight settable composition further comprises at leastone additive selected from the group consisting of crystalline silica,fumed silica, silicates, salts, fibers, hydratable clays, shale,calcined shale, vitrified shale, microspheres, diatomaceous earth,natural pozzolan, cement kiln dust, resins, and any combination thereof.11. The method of claim 1, wherein the lightweight settable compositiondevelops a 24-hour compressive strength of about 100 psi after mixingthe pumice and the calcium activator with the water.
 12. A method ofremedial cementing in a subterranean formation comprising: providing alatex-free lightweight settable composition comprising pumice, a calciumactivator, shale in an amount of about 40% to about 100% by weight ofthe pumice, zeolite in an amount of about 40% to about 100% by weight ofthe pumice, and water, wherein the lightweight settable composition hasa density of less than about 13.5 pounds per gallon and is essentiallyfree of any additional cementitious components, wherein the lightweightsettable composition is foamed with a foaming additive and a gas; andplacing the lightweight settable composition into a void or crack in thesubterranean formation, a gravel pack, a conduit, a cement sheath, or amicroannulus.
 13. The method of claim 12, wherein the water is presentin an amount in a range of from about 40% to about 200% by weight of thepumice.
 14. The method of claim 12, wherein the calcium activator ispresent in an amount of about 0.1% to about 25% by weight of the pumice.15. The method of claim 12, wherein the calcium activator comprises amaterial selected from the group consisting of calcium formate, lime,hydrated lime, and any combination thereof.
 16. The method of claim 12,wherein the lightweight settable composition further comprises at leastone additive selected from the group consisting of amorphous silica, flyash, metakaolin, perlite, rice hull hush, a swellable particulateelastomer, and any combination thereof.